This invention relates in general to an apparatus and method for balancing an article, such a tube for use in a vehicular driveshaft assembly, for rotation about an axis. More specifically, this invention relates to an apparatus and method for automatically balancing such an article for rotation about an axis using digital imaging and ultrasonic thickness measuring techniques.
In most rear wheel drive vehicles, a source of rotational energy, such as an internal combustion or diesel engine, is located near the front of the vehicle. The engine is connected by means of a driveshaft assembly to rotate one or more driven wheels, which are located near the rear of the vehicle. The driveshaft assembly typically extends between an output shaft of a transmission, which is connected to and rotatably driven by the engine, and an input shaft of a differential, which is connected to rotatably drive the driven wheels. In some vehicles, the distance separating the transmission and the differential is relatively short. In these vehicles, the driveshaft assembly can be formed from a single, relatively long driveshaft tube having first and second universal joints that connect the ends of the driveshaft tube to the output shaft of the transmission and the input shaft of the differential. In other vehicles, the distance separating the transmission and the differential is relatively long, making the use of a single driveshaft impractical. In these vehicles, the driveshaft assembly can be formed from a plurality (typically two) of separate, relatively short driveshaft tubes. The driveshaft tubes are connected together by a first universal joint, and second and third universal joints are provided to connect the ends of the driveshaft tubes to the output shaft of the transmission and the input shaft of the differential.
Ideally, each of the driveshaft tubes would be formed in the shape of a cylinder that is absolutely round, absolutely straight, and has an absolutely uniform wall thickness. Such a perfectly shaped driveshaft tube would be precisely balanced for rotation and, therefore, would not generate any undesirable noise or vibration during use. In actual practice, however, the driveshaft tubes usually contain variations in roundness, straightness, and wall thickness that result in minor imbalances when rotated at high speeds. To prevent such imbalances from generating undesirable noise or vibration when rotated during use, therefore, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft tube. The balance weights are sized and positioned to counterbalance the imbalances of the driveshaft tube such that it is balanced for rotation during use.
Traditionally, the balancing process has been performed through the use of a conventional balancing machine. The balancing machine includes a pair of fittings that are adapted to support the ends of the driveshaft tube thereon. The balancing machine further includes a motor for rotating the driveshaft tube at a predetermined speed. As the driveshaft tube is rotated, the balancing machine senses vibrations that are caused by imbalances in the structure of the driveshaft tube. The balancing machine is responsive to such vibrations for determining the size and location of one or more balance weights that, if secured to the driveshaft, will minimize these imbalances. The rotation of the driveshaft tube is then stopped to allow such balance weights to be secured to the outer surface of the driveshaft tube in a conventional manner, such as by welding, adhesives, and the like. The driveshaft tube is again rotated to confirm whether proper balance has been achieved or to determine if additional balance weights are required. A number of such balancing machines of this general structure and method of operation are known in the art.
Although such prior art balancing machines have been effective, this balancing process has been found to be relatively slow and inefficient. This is because each driveshaft tube must usually be rotated and measured at least two times, a first time to measure the imbalances and determine the size and location of the balance weights, and a second time to confirm that proper balance has been achieved after the balance weights have been secured thereto. This time consuming process is particularly problematic in the context of balancing vehicular driveshaft tube, which are typically manufactured in relatively large volumes. Thus, it would be desirable to provide an improved apparatus and method for quickly and efficiently balancing an article, such a tube for use in a vehicular driveshaft assembly, for rotation about an axis.
This invention relates to an improved apparatus and method for quickly and efficiently balancing an article, such a tube for use in a vehicular driveshaft assembly, for rotation about an axis. The apparatus includes a pair of supports that are adapted to engage and support the ends of the driveshaft tube and to effect selective rotational and axial movement thereof. A system is provided for generating a representation of the shape of the outer surface of the driveshaft tube, such as by using a laser stripe generator and a digital camera. The laser stripe generator projects a relatively thin line of visible light onto the outer surface of the driveshaft tube. The digital camera receives the relatively thin visible line of light as it is reflected from the outer surface of the driveshaft tube and digitizes the reflected image into electrical signals. The apparatus further includes a system for generating a representation of the wall thickness of the driveshaft tube, such as by using an ultrasonic transducer. The signals from the digital camera and the ultrasonic transducer are fed to an electronic controller, which correlates such signals to generate an electronic three dimensional representation of the physical shape of the driveshaft tube. By summing all of such correlations together for the entire outer surface of the driveshaft tube, an electronic three dimensional representation of the physical shape of the driveshaft tube can be generated. The electronic controller then generates a mass or weight distribution representation of the driveshaft tube which can be analyzed to determine where imbalances are present. Based upon these calculations, the electronic controller can further determine the size and position of the balance weights to be secured to the driveshaft tube to counterbalance these imbalances. Such size and position information can be relayed to an operator in any conventional manner using an output device.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.